Reconstruction of the spatial distribution of radioactive contamination from aerial survey and from a stationary array of directional detectors

Natural Resources Canada has responsibility for mobile survey in response to radiological emergencies in Canada. The team maintains both aerial and truckborne survey systems based on large volume NaI(Tl) gamma detectors integrated with instrumentation for position detection and for environmental monitoring. The team must be able to map the activity concentration of an extended source, whether arising from the detonation of a radiological dispersal device, or a nuclear power plant accident. We have developed novel methods to treat both aerial and truckborne mobile survey datasets. A deconvolution method applied to aerial survey data results in a finer spatial resolution of the measurement. In the truckborne setup, four detectors are oriented vertically in a self-shielding configuration to provide an azimuthal direction reading. In a first step toward development of a method for spatial inversion of truckborne survey results, we have treated a mobile traverse with one system in different locations at different times as a stationary array of multiple systems in different locations at one time. A spatial inversion method then allows for extrapolation of the activity concentration measurement to positions a distance from the traverse. Here, we present these two new methods for spatial reconstruction, and show results for distributed radioactivity from synthetic data.